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Reflective Optical Sensor SFH 7740

The SFH 7740 is a very small reflective optical sensor for short distances with digital output. With dimensions of only 3.7 × 3.7 × 1 mm, and surface-mount solder contacts, the device may be integrated in applications where reflective sensors have previously not been considered.

This device was conceived to detect the position of mechanical parts. Two example applications are: a short-distance (mm regime) proximity sensor (e.g. to detect whether a cover is open or closed), or a sensor that detects the relative position of a structured surface (e.g. slider-position in cellular phones). With a bright, highly reflective object is in front of the sensor the output switches to high (“H), and with a dark object (or no object at all) in front of the sensor the output is low (“L”).

This application note is structured as follows:

General description of the part is design and operating principle

Application circuit recommendations

Customization/calibration to account for optical properties of the application